PDF Guru is like Chrome for PDF readers

This is a quick post to highlight an excellent new PDF reader on macOS called PDF Guru (iTunes store). It is a recently revamped version of PDF Reader X.

I’ve only used it for a week, but it’s the best PDF reader I’ve experienced for reading academic articles. It’s snappy and reminds me of Chrome when it first came out. Draggable tabs. Split view. Plays well with Zotero. Can easily add native PDF annotation and search through the existing ones. (And it saves annotations fast when you close the file.Competitors either do this slowly or, like Skim, use a non-native annotation format that can’t be read by other PDF readers.a  ) The UI for “find” displays a lot of info intuitively.Edit 2018-1-12: And you can search for any unicode character! Really useful for searching a document for math.b   Everything is just nicely designed. I haven’t yet run into a limitation on the free version, but it’s worth upgrading to Pro to support the developer (only $20).



Beware that this is the first version following a big re-write of PDF Reader X, and it’s not completely stable. I’ve gotten it to crash a few times, but the developer has been very responsive to feedback and I’d wager on the stability improving soon. (Edit 2018-1-7: After upgrading to the new version, 3.0.20A, a couple weeks ago, I haven’t experienced any crashes. Looks stable.)

I’m advertising Guru because I think the current selection of PDF readers for academic reading is pretty bad.I have no connection to the developer.c   I strongly prefer Guru (instability and all) over these other PDF readers on maxOS that I have tried: FoxIt, Preview, Adobe Acrobat Reader, and Skim.… [continue reading]

Links for November 2017

  • For several months, Fermat’s Library has offered a Chrome extension called Librarian for browsing PDFs on the arXiv that automatically parses references to clickable journal links and bibtex entries. Very recently they added the ability to publicly comment, visible to anyone else running Librarian. Should be lower friction than commenting on (also excellent) SciRate.
  • Just heard about this story showing that the AZ governor means business:

    Three weeks into his new job as Arizona’s governor, Doug Ducey made a move that won over Silicon Valley and paved the way for his state to become a driverless car utopia.

    It was January 2015 and the Phoenix area was about to host the Super Bowl. Mr. Ducey learned that a local regulator was planning a sting on Lyft and Uber drivers to shut down the ride-hailing services for operating illegally. Mr. Ducey, a Republican who was the former chief executive of the ice cream chain Cold Stone Creamery, was furious.

    “It was the exact opposite message we should have been sending,” Mr. Ducey said in an interview. “We needed our message to Uber, Lyft and other entrepreneurs in Silicon Valley to be that Arizona was open to new ideas.” If the state had a slogan, he added, it would include the words “open for business.”

    Mr. Ducey fired the regulator who hatched the idea of going after ride-hailing drivers and shut down the entire agency, the Department of Weights and Measures. By April 2015, Arizona had legalized ride-sharing.

  • The last time a US Air Force bomber downed an enemy plane using its tail gun was 1972, but B-52s — which have been in service for a baffling 65 years — still carried (highly modernized) tail guns up until 1991 when a US air-to-surface missile mistakenly locked on to the tail gun’s radar and nearly destroyed the plane.
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Branches as hidden nodes in a neural net

I had been vaguely aware that there was an important connection between tensor network representations of quantum many-body states (e.g., matrix product states) and artificial neural nets, but it didn’t really click together until I saw Roger Melko’s nice talk on Friday about his recent paper with Torlai et al.:There is a title card about “resurgence” from Francesco Di Renzo’s talk at the beginning of the talk you can ignore. This is just a mistake in KITP’s video system.a  





[Download MP4]   [Other options]


In particular, he sketched the essential equivalence between matrix product states (MPS) and restricted Boltzmann machinesThis is discussed in detail by Chen et al. See also good intuition and a helpful physicist-statistician dictionary from Lin and Tegmark.b   (RBM) before showing how he and collaborators could train an efficient RBM representations of the states of the transverse-field Ising and XXZ models with a small number of local measurements from the true state.

As you’ve heard me belabor ad nauseum, I think identifying and defining branches is the key outstanding task inhibiting progress in resolving the measurement problem. I had already been thinking of branches as a sort of “global” tensor in an MPS, i.e., there would be a single index (bond) that would label the branches and serve to efficiently encode a pure state with long-range entanglement due to the amplification that defines a physical measurement process. (More generally, you can imagine branching events with effects that haven’t propagated outside of some region, such as the light-cone or Lieb-Robinson bound, and you might even make a hand-wavy connection to entanglement renormalization.)… [continue reading]

Links for October 2017

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Models of decoherence and branching

[This is akin to a living review, which will hopefully improve from time to time. Last edited 2020-4-8.]

This post will collect some models of decoherence and branching. We don’t have a rigorous definition of branches yet but I crudely define models of branching to be models of decoherenceI take decoherence to mean a model with dynamics taking the form U \approx \sum_i \vert S_i\rangle\langle S_i |\otimes U^{\mathcal{E}}_i for some tensor decomposition \mathcal{H} = \mathcal{S} \otimes \mathcal{E}, where \{\vert S_i\rangle\} is an (approximately) stable orthonormal basis independent of initial state, and where \mathrm{Tr}[ U^{\mathcal{E}}_i \rho^{\mathcal{E} \dagger}_0 U^{\mathcal{E}}_j ] \approx 0 for times t \gtrsim t_D and i \neq j, where \rho^{\mathcal{E}}_0 is the initial state of \mathcal{E} and t_D is some characteristic time scale.a   which additionally feature some combination of amplification, irreversibility, redundant records, and/or outcomes with an intuitive macroscopic interpretation.

(Note in particular that I am not just listing models for which you can mathematically take a classical limit (\hbar\to 0 or N\to\infty) and recover the classical equations of motion; Yaffe has a pleasingly general approach to that task [1], but I’ve previously sketched why that’s an incomplete explanation for classicality.)

I have the following desiderata for models, which tend to be in tension with computational tractability:

  • physically realistic
  • symmetric (e.g., translationally)
  • no ad-hoc system-environment distinction
  • Ehrenfest evolution along classical phase-space trajectories (at least on Lyapunov timescales)

Regarding that last one: we would like to recover “classical behavior” in the sense of classical Hamiltonian flow, which (presumably) means continuous degrees of freedom.… [continue reading]

Comments on Weingarten’s preferred branch

[Added 2022-March-13: Weingarten has a new paper, discussed by me here, that mostly supercedes the content of this post.]

A senior colleague asked me for thoughts on this paper describing a single-preferred-branch flavor of quantum mechanics, and I thought I’d copy them here. Tl;dr: I did not find an important new idea in it, but this paper nicely illustrates the appeal of Finkelstein’s partial-trace decoherence and the ambiguity inherent in connecting a many-worlds wavefunction to our direct observations.


We propose a method for finding an initial state vector which by ordinary Hamiltonian time evolution follows a single branch of many-worlds quantum mechanics. The resulting deterministic system appears to exhibit random behavior as a result of the successive emergence over time of information present in the initial state but not previously observed.

We start by assuming that a precise wavefunction branch structure has been specified. The idea, basically, is to randomly draw a branch at late times according to the Born probability, then to evolve it backwards in time to the beginning of the universe and take that as your initial condition. The main motivating observation is that, if we assume that all branch splittings are defined by a projective decomposition of some subsystem (‘the system’) which is recorded faithfully elsewhere (‘the environment’), then the lone preferred branch — time-evolving by itself — is an eigenstate of each of the projectors defining the splits. In a sense, Weingarten lays claim to ordered consistency [arxiv:gr-qc/9607073] by assuming partial-trace decoherenceNote on terminology: What Finkelstein called “partial-trace decoherence” is really a specialized form of consistency (i.e.,[continue reading]

Symmetries and solutions

Here is an underemphasized way to frame the relationship between trajectories and symmetries (in the sense of Noether’s theorem)You can find this presentation in “A short review on Noether’s theorems, gauge symmetries and boundary terms” by Máximo Bañados and Ignacio A. Reyes (H/t Godfrey Miller).a  . Consider the space of all possible trajectories q(t) for a system, a real-valued Lagrangian functional L[q(t)] on that space, the “directions” \delta q(t) at each point, and the corresponding functional gradient \delta L[q(t)]/\delta q(t) in each direction. Classical solutions are exactly those trajectories q(t) such that the Lagrangian L[q(t)] is stationary for perturbations in any direction \delta q(t), and continuous symmetries are exactly those directions \delta q(t) such that the Lagrangian L[q(t)] is stationary for any trajectory q(t). That is,

(1)   \begin{align*} q(t) \mathrm{\,is\, a\,}\mathbf{solution}\quad \qquad &\Leftrightarrow \qquad \frac{\delta L[q(t)]}{\delta q(t)} = 0 \,\,\,\, \forall \delta q(t)\\ \delta q(t) \mathrm{\,is\, a\,}\mathbf{symmetry} \qquad &\Leftrightarrow \qquad \frac{\delta L[q(t)]}{\delta q(t)} = 0 \,\,\,\, \forall q(t). \end{align*}

There are many subtleties obscured in this cartoon presentation, like the fact that a symmetry \delta q(t), being a tangent direction on the manifold of trajectories, can vary with the tangent point q(t) it is attached to (as for rotational symmetries). If you’ve never spent a long afternoon with a good book on the calculus of variations, I recommend it.

Footnotes

(↵ returns to text)

  1. You can find this presentation in “A short review on Noether’s theorems, gauge symmetries and boundary terms” by Máximo Bañados and Ignacio A. Reyes (H/t Godfrey Miller).
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Links for August-September 2017

  • Popular-level introduction to the five methods used to identify exoplanets.
  • Another good profile of the SEP.
  • ArXiv gets some money to improve stuff.
  • Flying fish are hard to believe. It’s something of a tragedy that fish capable of long-distance flight never evolved (that we know of?). They are so bird like it’s startling, and this ability has evolved independently multiple times.
  • In addition to Russia and China, the US also at one time had ICBMs deployed by rail.
  • On nuclear decommissioning:

    For nuclear power plants governed by the United States Nuclear Regulatory Commission, SAFSTOR (SAFe STORage) is one of the options for nuclear decommissioning of a shut down plant. During SAFSTOR the de-fuelled plant is monitored for up to sixty years before complete decontamination and dismantling of the site, to a condition where nuclear licensing is no longer required. During the storage interval, some of the radioactive contaminants of the reactor and power plant will decay, which will reduce the quantity of radioactive material to be removed during the final decontamination phase.

    The other options set by the NRC are nuclear decommissioning which is immediate dismantling of the plant and remediation of the site, and nuclear entombment which is the enclosure of contaminated parts of the plant in a permanent layer of concrete.Mixtures of options may be used, for example, immediate removal of steam turbine components and condensors, and SAFSTOR for the more heavily radioactive containment vessel. Since NRC requires decommissioning to be completed within 60 years, ENTOMB is not usually chosen since not all activity will have decayed to an unregulated background level in that time.

  • The fraction of the federal budget devoted to NASA peaked in 1966, three years before the Moon landing.
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